1. Field of the Invention:
The present invention relates to a communication network control system, a radio communication apparatus used in the system, a communication network control method, and a radio base station.
2. Description of Background Technology:
The number of subscribers of cellular phones has increased yearly and recently exceeded 90 million. That is, about ⅔ the population of Japan possess cellular phone sets. On the other hand, the communication network resources are finite, and many cellular phone owners simultaneously communicate in a densely populated area, a disaster area, or the like, in particular. This may cause congestion in the communication network.
As a related technique for avoiding such communication network congestion, Japanese Unexamined Patent Publication (KOKAI of the Japanese Patent Application) No. 05-252103 (Patent Document 1) discloses a digital car phone system which increases the number of channels at the time of traffic congestion in a radio base station. In this system, upon detecting traffic congestion, a radio base station transmits a half rate request. signal to a car phone terminal. Upon receiving the half rate request signal, the car phone terminal starts half-rate communication through the radio base station.
Japanese Unexamined Patent Publication (KOKAI of the Japanese Patent Application) No. 05-183495 (Patent Document 2) discloses a method of performing congestion control in radio communication. According to this method, a base station calculates the traffic amount of a radio channel by detecting the communication schemes used by terminals under communication and the number of terminals. The base station then imposes call limitation on terminals on the basis of the communication scheme used by the terminals under communication, the number of terminals, and the calculated traffic amount.
In addition, Japanese Unexamined Patent Publication (KOKAI of the Japanese Patent Application) No. 2004-15761 (Patent Document 3) discloses a congestion control system in radio access. In this system, upon detecting congestion, a terminal notifies a radio base station of the corresponding information. Upon receiving the congestion notification, the radio base station instructs a transcoder to suppress the bit rate of a speech CODEC (Coder/Decoder), thereby canceling the congestion state.
According to the background technology described above, although congestion occurs on the circuit domain side used in general speech communication, sufficient capacity may remain on the packet domain side used in packet communication for e-mail and the like.
At the time of a disaster, e.g., an earthquake, when it is expected that communication network congestion occurs, nobody can afford to take time to input an e-mail message, and hence it is preferable to allow speech communication.